Crocodile (train protection system)
The crocodile can provide two different pieces of information to the driver, according to the aspect of the corresponding signal: Communication between the ground-based signalling system and the in-cab equipment is made by the crocodile, an electrical contact placed between the rails and a metallic brush mounted beneath the locomotive cab.It is distinctively French, originating on the Chemins de fer du Nord around 1872, spreading throughout France[1] and penetrating into Belgium and Luxembourg after 1900.It was intended principally to provide evidence of the alertness of the driver, not to act to control a train automatically.Originally it was placed 100–200 metres in front of a distant signal, usually a red disc of "deferred stop".If a signal changed suddenly to a caution or danger aspect in the face of the driver, it would appear that they had not noticed it and had been surprised, when that was not the case.